I. Field of the Invention
The present invention relates to previewing apparatus for previewing color separation flats of respective colors to determine if negatives located on each flat (and representing pictorial or graphic information) are in registration with one another. The negatives are nominally located at predetermined locations on the flats (each flat representing, for example, a therewith for vacuum-contacting said flats are formed in said flat setting table. More specifically, the present invention relates to a previewing apparatus for performing such previewing using a color CRT (cathode-ray tube) monitor.
II. Description of the Prior Art
In order to prepare a printing plate, it is conventionally known, as shown in FIG. 1, to attach a color separation film 1 (obtained by color separation of an original) or characters 2 for each color on a single transparent film 3 to form a color separation flat.* In this case, it is necessary to check if the images of the respective color separation films on each flat have an accurate registration with the color separation films on the remaining flats. As a method for performing this, a method is known according to which, if the four colors of yellow, magenta, cyan and black are involved, the flat corresponding to one of these four colors is selected as a key or standard flat. Another flat is superposed on this standard flat to check registration. Other printing plate films are also superposed on the standard for checking the registration in a similar manner. FNT *This flat, as an example in the case of offset printing process, is contacted to a PS plate (presensitized plate) which is exposed to light through the flat. The exposed PS plate is developed to be used as a printing plate for the offset printing process.
In this case, however, since both the standard flat and other flats are positives or negatives, it is difficult to check the registration.
As a method to eliminate this drawback, there is known another method, if the four colors of yellow, magenta, cyan and black are involved, according to which a film of an inverted image is prepared from one flat to provide a master flat as a standard, and other flats are superposed on this master flat to check for the registration in the manner described with the method described above. In this case, since the master flat as the standard and the other flats are in opposite relationships: if one is the positive, the other is the negative and vice versa, it is easy to check the registration. However, since extra film is required for preparing the master flat, additional cost and time are involved.
An apparatus is disclosed in U.S. Pat. No. 3,972,066, according to which color separation films separated into the four colors of Y (yellow), M (magenta), C (cyan), and BL (black) are photographed by a television camera and displayed on a color CRT monitor in a composition of colors.
The apparatus disclosed in this patent is designed to estimate the tone of the actual printed matter from the color separation films. With this apparatus, it is difficult to check the registration of flats which are obtained by attaching the color separation films on big transparent film bases in a simple manner and a short period of time and with high accuracy. In other words, the apparatus described in this U.S. patent is essentially contemplated to check the color separation conditions of the color separation films themselves. According to this apparatus, the color separation films corresponding to four colors are each separately photographed by a single fixed camera to store the image information in a memory device, and the stored image information is displayed on the color CRT monitor. Therefore, the area of the image to be displayed is limited to a certain area (i.e., only a portion of the area can be viewed at any given time). This apparatus is not suitable for checking the registration of a flat which requires checking over a wide area with high precision.
The checking of the flat includes, in addition to the checking of the registration, the checking of the separation quality, copy, dummy, screen tint and other instructions for completeness and accuracy. However, no conventional apparatus has been seen which can accomplish checking of various items as described above which good efficiency and in a simple manner.